Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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211
FXUS66 KSEW 202224
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
224 PM PST Mon Jan 20 2020

.SYNOPSIS...A weak front will dissipate over the western portion
of the area tonight. Additional systems will move through the
region Tuesday through the rest of the week with lowland rain and
fluctuating snow levels in the mountains.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...A weak cold front is
over western WA today with scattered showers across the region.
Showers will mostly affect the coast overnight as this system
continues to dissipate.

A stronger frontal system will push inland on Tuesday for more
rain, a chance of thunderstorms along the coast, and heavy snow
in the mountains. Snow levels are around 3,000 feet with highest
snow amounts in the North Cascades at Mount Baker - a Winter Storm
Warning is in effect. East winds will keep pass temperatures below
freezing through the day with snow affecting both Stevens and
Snoqualmie Pass. Snoqualmie Pass will likely see a change over to
rain (or a rain/snow mix) Tuesday night as winds become more
westerly. Down in the lowlands, expect rain and breezy winds
through the period with temperatures close to normal.

Wednesday and Thursday brings warmer conditions with snow levels
rising (to 5000-6000 feet). Several wet Pac Systems will clip the
area for period of heavy rain, especially over the coast and
mountains. Rainfall totals in the mountains will be 3-4" with
higher amounts possible in the Olympics. This will force sharp
rises on the rivers with minor flooding possible. Expect mild
temps in the lowlands with highs reaching the lower 50s. 33

.LONG TERM /FRIDAY THROUGH MONDAY/...Periods of heavy rain
will continue into Friday, and possibly Saturday, as more wet Pac
systems roll through the region. Rivers will continue to run high
with flooding still a threat. A break in the pattern Saturday
night and Sunday will bring a brief respite. A cooler upper trough
will bring more rain and mountain snow early next week. 33

&&

.AVIATION...A frontal boundary will continue to weaken across the
area through the evening. Rain showers continue to develop in the
vicinity of the frontal boundary, with best chances for rain in the
HQM and BLI areas. Showers will remain in the vicinity of the TAF
sites near Puget Sound, and will have to monitor for potential
amendments to include brief rain showers. Ceilings are mostly VFR,
with the exception of HQM at MVFR, and should see these trends
continue overnight barring any brief rain shower. The next organized
front will approach the area on Tuesday, bringing widespread rain
inland early in the morning hours, along with ceiling reductions to
MVFR. Rain will become more scattered through the day, with thunder
possible near HQM. Winds light and variable this afternoon, becoming
more S/SE overnight (5-10kts) and breezy by Tuesday morning.
Sustained winds on Tuesday 10-15kts with gusts 20-25kts.

KSEA...VFR ceilings through much of the overnight, with scattered
showers in the vicinity. Next round of widespread rain expected by
early Tuesday morning, likely lowering cigs to MVFR. Rain will
become scattered by the afternoon. Winds S/SE 5-10kts overnight,
increasing to 10-15kts Tuesday morning with a few gusts near 20kts.

Kovacik

&&

.MARINE...The latest surface analysis from WPC depicts a weakening
frontal boundary across western Washington this afternoon. MRMS
radar imagery compliments this analysis well with scattered rain
showers across the interior waters, and more widespread stratiform
rain across the southern coastal waters. This activity should
continue through the evening hours, with possible visibility
reductions in some of the showers.

A look upstream reveals a more robust weather system just west of
the outer coastal waters. The frontal boundary associated with this
weather system will make eastward progress overnight tonight and
through the day on Tuesday. Gradients appear rather strong in the
vicinity of the frontal system, with a healthy increase in wind
speed expected overnight and Tuesday. The first area to experience
stronger winds will be the coastal waters where winds should pick up
to Gale around midnight. Soon after, winds will pick up across the
interior waters, mostly to SCA. The exception could be the eastern
Strait along with far eastern portions of the central Strait, where
the 1 & 4km WRF guidance, along with the hi-red ARW suggest gale
force winds. Have issued a Gale Warning for these waters through
Tuesday afternoon. Winds will likely remain SCA for most waters thru
wednesday morning before briefly relaxing ahead of the next weather
system.

In addition to the winds, swells will increase through the day on
Tuesday to roughly between 14-17 feet. This will continue rough bar
conditions near Grays Harbor, which has lead to the extension of the
SCA already in place. Seas should subside on Wednesday. Active
marine weather is likely to continue off and on through the much of
the week as several weather system moves across the area.

Kovacik

&&

.HYDROLOGY...A period of warming, rising snow levels, and heavy
rain in the mountains will force sharp rises on the rivers flowing
off the Olympics and Cascades in western Washington. Snow levels
will rise to around 5,000 to 6,000 feet with 3 to 6 inches of rain
in the mountains Wednesday through early Friday. Minor flooding
is possible on several rivers as a result. Rivers may be flowing
high through the weekend before receding.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 4 AM Tuesday to 4 AM PST Wednesday
     for Cascades of Pierce and Lewis Counties-Cascades of
     Snohomish and King Counties.

     Winter Storm Warning from 4 AM Tuesday to 4 AM PST Wednesday for
     Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 10 PM PST this evening for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm.

     Gale Warning from 10 PM this evening to 4 PM PST Tuesday for
     Coastal Waters From Cape Flattery To James Island 10 To 60
     Nm-Coastal Waters From Cape Flattery To James Island Out 10
     Nm-Coastal Waters From James Island To Point Grenville 10
     To 60 Nm-Coastal Waters From James Island To Point
     Grenville Out 10 Nm-Coastal Waters From Point Grenville To
     Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 10 AM PST Wednesday for Grays Harbor
     Bar.

     Gale Warning from 10 PM this evening to 7 PM PST Tuesday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 10 PM this evening to 1 AM PST
     Wednesday for Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory from 10 PM this evening to 4 PM PST Tuesday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 1 AM Tuesday to 4 AM PST Wednesday for
     Admiralty Inlet-Puget Sound and Hood Canal.

&&

$$

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